Crain 18" Scribing Tool accurately scribes longer widths from 2" to 16". It has a knurled two-part brass thumb knob for all necessary adjustments, with no screwdriver required. The top portion adjusts the pin height based on the material thickness, and the bottom portion sets the offset distance between the needle and the guide that is being used. Includes a rounded end guide for walls and a bottom guide for seam scribing that runs along the edge of the bottom piece of material as the top piece is being scribed. Needles are replaceable.